The long-range goal of this project is to understand the biological significance of visual pigments as evolutionary adaptations to the visual requirements of animals. The inheritance of visual proteins (opsins) will be studied in poeciliid fishes. Fertile hybrids can be produced between parental stocks that have different visual pigments. The patterns of inheritance will be investigated in detail. Related questions concerning the relative influence of genetic background and environment over the interconversion of retinene sub 1 and retinene sub 2 will also be investigated. Laboratory experiments will be correlated with field studies of the visual pigments of cyprinid fishes. The photic environments in which these animals live will be measured and related to the biochemical findings.